Ever stricter statutory regulations regarding permissible pollutant emissions from motor vehicles which have internal combustion engines make it necessary to keep the pollutant emissions as low as possible during operation of the internal combustion engine. This can be achieved, on the one hand, in that the pollutant emissions which arise during combustion of the fuel/air mixture in the respective cylinder of the internal combustion engine are reduced. On the other hand, exhaust treatment systems which convert the pollutant emissions which are produced during combustion of the fuel/air mixture in the respective cylinder into harmless substances are used in internal combustion engines. For this purpose, catalytic converters which convert carbon monoxide, hydrocarbons and nitrogen oxides into harmless substances are used. Both targeted influencing of the production of the pollutant emissions during combustion and the conversion of the pollutant components with a high level of efficiency by an exhaust catalytic converter require a very precisely adjusted air/fuel ratio in the respective cylinder.
The SAE International publication “A Metal Substrate with Integrated Oxygen Sensor; Functionality and Influence on Air/Fuel Ratio Control”, Mats Laurell et al., SAE 2003-01-0818, describes a device for an internal combustion engine with a catalytic converter in the exhaust system. A linear lambda sensor is arranged in the exhaust system upstream from the exhaust catalytic converter. Also arranged in the exhaust catalytic converter are a first and a second binary lambda probe. The binary lambda probe is used for trimming the probe signal from the linear lambda sensor. The measured signal from the linear lambda sensor which is thus trimmed is the control variable of the lambda controller.
From the textbook “Handbuch Verbrennungsmotor”, edited by Richard von Basshuysen, Fred Schäfer, 2nd edition, Vieweg & Sohn Verlagsgesellschaft mbH, June 2002, pages 559-561, a linear lambda control system is known which has a linear lambda probe arranged upstream of an exhaust catalytic converter, and a binary lambda probe which is arranged downstream of the exhaust catalytic converter. A target lambda value is filtered by a filter which takes account of the delays and the sensor behavior. The thus filtered lambda target value is the control variable of a PII2D-Lambda controller whose manipulated variable is an injection quantity correction.
Also known from the textbook “Handbuch Verbrennungsmotor”, edited by Richard von Basshuysen, Fred Schäfer, 2nd edition, Vieweg & Sohn Verlagsgesellschaft mbH, June 2002, pages 559-561, is a binary lambda control system which has a binary lambda probe arranged upstream of the exhaust catalytic converter. The binary lambda control system also comprises a PI controller wherein the P and I components are stored in engine characteristic maps as engine speed and load. With the binary lambda control, excitation of the catalyst, also denoted as lambda oscillation, is implicitly produced by two-step control. The amplitude of the lambda oscillation is set to about three percent.